1. Technical Field
The present disclosure relates to a MEMS device having a suspended diaphragm and to the manufacturing process thereof. In particular, the following description makes reference, without this implying any loss in generality, to a MEMS pressure sensor of a packaged type.
2. Description of the Related Art
Sensors including micromechanical structures manufactured, at least in part, using semiconductor materials and MEMS (micro-electro-mechanical systems) technology are increasingly used, due to the advantageous characteristics of small dimensions, low manufacturing costs, and flexibility.
Specifically, pressure sensors manufactured using the MEMS technology typically find use in the medical field, in household apparatuses, in consumer electronics (cellphones, personal digital assistants—PDAs), and in the automotive field. In particular, in the latter sector, pressure sensors are traditionally used for detecting the pressure of vehicle tires, and are used by the control unit for signaling alarms. Pressure sensors are also used for monitoring the pressure of air-bags, for controlling the failure pressure of the ABS, and for monitoring the engine-oil pressure, the fuel-injection pressure, etc.
A MEMS sensor generally comprises a micromechanical detection structure, which transduces a mechanical quantity to be detected (for example, a set of acoustic waves, a pressure, etc.) into an electrical quantity (for example, correlated to a capacitive variation); and an electronic reading circuit, usually made as an ASIC (Application-Specific Integrated Circuit), which performs processing operations (including amplification and filtering) of the electrical quantity and supplies an electrical output signal of an analogue type—for example, a voltage—or a digital type—for example, a PDM (Pulse Density Modulation) signal. The electrical signal, possibly further processed by an electronic interface circuit, is then made available to an external electronic system, for example a microprocessor control circuit of the electronic apparatus incorporating the sensor.
To detect the mechanical quantity, MEMS sensors of the considered type comprise a diaphragm formed in or on a semiconductor die and suspended over a cavity. The diaphragm faces the external environment or is in communication with the latter through a fluidic path, as shown, for instance, in U.S. Pat. No. 8,049,287, filed in the name of the present applicant, disclosing a detection structure including a MEMS pressure sensor, of a differential capacitive type. In particular, in U.S. Pat. No. 8,049,287, the diaphragm faces a chamber formed in a protective cap fixed at the top to the die and perforated for exposure to the surrounding environment or faces a cavity etched from the back of the die and connected with the outside by a hole which extends through supporting elements.
Known MEMS sensors, albeit widely used and satisfactory, may be improved in particular as regards insensitivity to packaging stress and at the same time robustness of the sensitive part.